To date, spin devices have utilized the rocket exhaust gases of the motor via vanes or fins located in the divergent section of the nozzle near the nozzle exit plane. The rockets incorporating this type of spin device were spun to the required spin sometimes during the flight phase. The purpose of spinning a fin stabilized free flight rocket is to nullify thrust misalignment, assymetrical aerodynamic forces and to some extent to reduce mallaunch. A further reduction in these errors which cause dispersion can be obtained by a rocket which is spun to its maximum spin rate at launch. The torque impulse required to spin a rocket to 15 or 20 rps in a short guidance length can be obtained with this type of spin device.
The in-tube or during guidance spin device of the present invention utilizes the features of the basic flow from the nozzle through a reflected shock wave, i.e. the increase in pressure and the straightening of the flow, to extract the required torque impulse to spin a rocket at a predetermined rate of spin. (typically, 15 rps in 4 feet of rocket travel) .